The in-situ delivery of therapeutic agents within the body of a patient is common in the practice of modern medicine. In-situ delivery of therapeutic agents is often implemented using medical devices that may be temporarily or permanently placed at a target site within the body. These medical devices can be maintained, as required, at their target sites for short or prolonged periods of time, in order to deliver therapeutic agents to the target site.
For example, in recent years, drug eluting coronary stents, which are commercially available from Boston Scientific Corp. (TAXUS), Johnson & Johnson (CYPHER) and others, have been widely used for maintaining vessel patency after balloon angioplasty. These products are based on metallic expandable stents with biostable polymer coatings that release antirestenotic drugs at a controlled rate and total dose.
Polymeric coatings for drug release from implantable or insertable devices such as stents may be less desirable with regard to long term vascular compatibility.
iMEDD, Inc. has created silicon membranes with parallel channels ranging from 4 to 50 nm. Diffusion rates of various solutes through such membranes have been measured and conform to zero-order kinetics in some instances. According to iMedd, the membranes can be engineered to control rates of diffusion by adjusting channel width in relation to the size of solutes. When the proper balance is struck, zero-order diffusion kinetics is possible. iMedd has produced a drug delivery device which consists of a drug-filled enclosure which is then fitted with a nanoporous membrane as the only connection between the internal reservoir of the device and the external medium.